A view of the old San Francisco Mint is seen through a stereoscopic viewer next to a copy of "Wasp", a mid-19th Century satirical magazine on Friday, Feb. 28, 2014 in Lafayette, Calif. Robert Chandler, a foremost historian of the Old West believes that the recently found stash of gold coins worth $10 million is likely to be the accumulation of someone's life savings.

Maybe it was stagecoach bandit Black Bart. Or Jesse James and his secret gang of post-Civil War Confederates. Or the clerk who ripped off the U.S. Mint in San Francisco in 1901.

Or maybe it was just some guy working in the mountains who poked away his cash in cans because he didn't trust banks.

The theories about how $10 million worth of 19th century gold coins came to be buried in a couple's Sierra Nevada backyard have proliferated like mushrooms since the pair revealed their find Tuesday. And the guesses about this whodunit don't focus just on famous outlaws.

Scores of people have contacted The Chronicle and the couple's coin dealer to say some long-lost relative or close pal stashed his or her money underground long ago, this must be it, and now they want their cut. That is guesswork at its essence, because the couple insist on anonymity and will say nothing about where they found the 1,427 gold coins stuffed into eight rusty cans, beyond that it's in the Gold Country.

"The response has been unbelievable. We've been contacted by individuals and media from literally all over the world, China to London, nonstop since the coins were revealed," said Don Kagin of Tiburon, a coin dealer who is shepherding the Saddle Ridge Hoard to sale on Amazon and through private channels. The find - believed to be the biggest cache of buried gold coins ever found in the U.S. - is named after the slope on the couple's property where the coins were found.

"The whole idea of buried treasure, the pot of gold at the end of the rainbow, has just captured everyone's imagination," Kagin said. "They can't stop speculating about it."

Robbery unlikely

The coins are dated from 1847 to 1894, and most of them are what are called Double Eagles, or $20 gold pieces, minted in San Francisco. About a third apparently were never circulated, and more than a dozen were judged by a rare-coin evaluator to be among the finest-preserved examples of their kind.

That's the kind of stash any self-respecting outlaw would have loved to get his mitts on. But local historians find theft theories unlikely.

"Black Bart? Nope. Train robbery? Nope. No go on stagecoach robberies in general, either," said Robert Chandler, retired senior researcher for Wells Fargo and an authority on Western history. "It is, of course, hard to say definitively. But that's how it looks."

Silver, not gold

About 300 stagecoaches and 20 trains were robbed in the late 19th and early 20th centuries in Northern California, according to John Boessenecker, a Western historian and author of "Badge and Buckshot: Lawlessness in Old California." But no rail heists match up well for the Saddle Ridge Hoard, and the stage robberies were either too small or involved more silver than gold, he said.

"It's definitely not bandit loot," Boessenecker said. "Robbers would get the stages when they were coming down the mountains, not up, and they not only mostly had a lot of silver, they only were good for $1,000 or so. Gold was too heavy then to take much more in something like a stagecoach.

"If it was a train robbery, this stash wouldn't make sense, because the coins that were found have a 50-or-so-year span, and most train money would be fresh coins being sent from the San Francisco mint."

Was it Black Bart?

Black Bart - real name Charles Earl Bowles - was the most famous and prolific stagecoach robber of that era, having held up 28 stages in Northern California from 1875 to 1883. However, the most he ever got away with was $5,000 in mixed silver and gold, and the rest of his holdups yielded just a few hundred bucks apiece - which he spent, Chandler said.

Bart was nabbed by Wells Fargo investigators as he strolled along San Francisco's Montgomery Street, did five years in San Quentin, then disappeared forever after his release in 1888, Chandler said.

"Nothing about Black Bart matches up for those coins," he said. "He is just a colorful character, which is why people bring him up."

Or Jesse James?

Equally colorful is outlaw Jesse James, and historical writer Warren Getler thinks there is a possibility he - or at least his clandestine outfit - had a hand in the Saddle Ridge treasure.

Getler says in his book "Rebel Gold" that James ran for years with a secret gang called the Knights of the Golden Circle that existed during the Civil War and afterward into at least the late 1800s. The gang buried hundreds of millions of dollars in gold bars and coins all over the United States - including in Northern California - in its effort to restart the Southern rebellion, Getler said.

Indeed, the Knights pulled off a well-documented stagecoach robbery of mostly silver 10 miles east of Placerville in 1864 at a spot called Bullion Bend.

"The KGC left caches of gold all over the West, and I'm telling you, this find fits the mold of a KGC cache," Getler said. One detail matches in particular, he said - the possible use of a marking stone.

The couple who found the stash while walking their dog in February 2013 said in a taped interview with Kagin that there was "an unusual angular rock up the hill from where the coins were buried."

"It wasn't until we made the find that we realized it might have been a marker," said the woman. "Starting at the rock, if you walk 10 paces toward the North Star, you wind up smack in the middle of the coins."

The Knights theory doesn't wash for Boessenecker.

"I just don't buy it," he said. "That gang was actually done by 1865, certainly in California, and most of these coins post-date that. It's a typical far-fetched conspiracy theory."

James was shot and killed on April 3, 1882, years before the newest coins in the hoard were minted. Getler says the gang continued to operate after the outlaw's death.

U.S. Mint theft

Another explanation put forth by hundreds of Internet commenters is that the cache is from a 1901 theft of 1,500 gold Double Eagle coins with a face value of $30,000 from the U.S. Mint in San Francisco. The number and face value is about the same as the Saddle Ridge Hoard, and though the mint's chief clerk, Walter Dimmick, was convicted of the crime, the booty was never recovered.

Kagin, however, said the mint explanation is unlikely because the coin dates are too spread out for a single haul like that. The coins are also too old for a 1901 heist, he said.

"It wouldn't be a mint robbery if it didn't have coins from at least the previous seven years, and the most recent coin in the hoard is from 1894," said Kagin, who in addition to being a dealer wrote the definitive "Private Gold Coins and Patterns of the United States."

Not so fast, says Dennis O'Donnell, an 86-year-old retired detective for the U.S. Mint in San Francisco who specialized in researching and solving coin thefts.

"Downstairs, we had vaults where we kept old coins that hadn't been put into circulation," he said. "Sometimes the auditors didn't see all the inventory. I wouldn't rule anything entirely out."

Maybe just a miser

Historians might have a better shot at tracking down the source of the loot if the couple would reveal where they found it. But that might also open them up to potentially messy ownership claims by descendants of whoever owned the land back in the 1800s, although Kagin said their attorneys have scoured public records and cleared the couple to sell the coins.

So for now, there seems to be only one likely scenario: Some no-name miser buried the treasure, meant to get back to it, but got cheated by death.

In the 19th century, miners and those paid in gold dust or nuggets would often tote their takes down to San Francisco and trade them in for sparkling new gold coins at the mint, Chandler said. Paper money didn't come into vogue in California until the late 1800s, so someone with a lot of cash and a distrust of banks - common in those boom-and-bust times - might well be hauling around a mix of circulated and freshly minted coins like those found in the Sierra.

"This probably wouldn't have been a regular workingman, since they only made about $40 a month," Boessenecker said. "But a merchant? Back then, they could make more than $1,000 a year. If you just spread these coins over, say, a 40-year period, it's about $700 being saved every year. So this could clearly just be a life's savings."

That's how looks to Kagin.

"We think it's someone in the mining industry who took his earnings or his bonus when he got it, filled those cans and buried them," the coin dealer said. "He probably meant to go back and dig them up, but met his demise and was single so nobody knew about it. That makes the most sense of all.

"But hey - it's just a theory."

Where's it from?

Some of the theories about how 1,427 gold coins came to be buried on a Gold Country property.

Theory: Stagecoach robber Black Bart buried the coins.

Problem: It doesn't fit his M.O.

Theory: Jesse James and his band of Confederate holdouts were responsible.